Nico Rosberg, 2010 Mercedes Grand Prix team-mate:

"It is fantastic that Michael is returning to Formula 1 and will be my team-mate at Mercedes Grand Prix Petronas. It's a great challenge for me to be up against one of the best drivers of all time. I'm sure that we will form a very strong partnership as he will have lost none of his speed! It is also great news for our sport and the fans."

Niki Lauda, triple F1 World Champion (speaking to Kicker magazine):

"His level is that of a seven-time world champion; he will be immediately competitive, because he was the best - on another level."

Eddie Irvine, former F1 team-mate at Ferrari (speaking to the BBC):

"There was no reason for him not to come back. Whatever aspect of F1 you're involved in, there's an intensity to it - every two weeks you're on show and you have to perform, and in the real world that just doesn't happen. It can take months or years before you get the rush that you get in Formula 1, and I think when he retired he had nothing else to do.

"The big problem is if he's head-to-head with someone like Lewis Hamilton; Lewis isn't going to back off, but Michael will have to because he's 41 years of age and the young guy will have the psychological advantage. I don't believe Michael is as fast as he was maybe seven years ago - if you watched the early days when he was at Benetton and Ferrari, his speed was quite sensational. He's probably lost a little bit of that and he's not at the peak of his game [anymore], there's no doubt about that, but he's still good enough to win races because he's such an immense talent.

"It's still four tyres, a steering wheel and an engine - and there's never been anyone better than Michael at making that package go as fast as possible. As I say, in a head-to-head with Lewis or some of the other young guys, I wouldn't put my money on Michael because he'd be mad to get really involved...but on pure speed he's probably up there with the best of them still."

Nigel Mansell, who won the 1992 F1 World Championship at the age of 39 (speaking to the Daily Mail):

"Age will not be a factor in Michael's story. It wouldn't surprise me if Michael challenged for another world championship. It doesn't matter what age you are as long as you are professional, committed and focussed. People have written Michael off as over the hill, [but] I look at it differently.

"Michael has tremendous experience and talent, and Mercedes will provide him with a fantastic package. He is extremely fit, and we can take his commitment and professionalism for granted. For me, there is no downside to this. He's won enough titles, so what does he have to worry about losing to anyone? It may take a few races to get to grips with his car, but after that it wouldn't surprise me if he was to challenge for his eighth title."

Jonathan Legard, BBC F1 commentator:

"It's great for Formula 1; it lifts everyone a little bit. It would seem that he's got the fitness, he's got the desire - and now he's got the contract. The fitness was a big worry in the summer - whether he was going to be fit enough [to substitute former Ferrari team-mate Felipe Massa] - but he was up there pretty much on the level straightaway, and remember, he took fitness levels to a new standard anyway. I wouldn't worry about him on that score, in fact I wouldn't worry about him at all. He's Michael Schumacher - he'll be good.

"He's achieved all of his successes with Ross Brawn, both at Benetton and at Ferrari, and is there going to be another glorious third chapter at Mercedes? If anyone can make it happen, it's Ross Brawn - just ask Jenson Button.

"[Schumacher] was the one, certainly when Lewis Hamilton was growing up, who set the benchmark. That's what Lewis would like to be. Now, he's up against the master. He didn't get the chance [to race against him] initially, but now they're head-to-head, and with [Fernando] Alonso at Ferrari and Button as well, it should be great."

Ted Kravitz, BBC F1 pit-lane reporter:

"Sporting comebacks are often ill-advised, but he just felt that his life was empty. When he was going to return to Formula 1 back in the summer I spoke to him and he said 'do you know what, before the neck injury I felt like I was alive again', so it's clearly been missing from his life. He's gone on to do motorbike races just to get that thrill of adrenaline, and even in Formula 1 he still thinks he can win; he wouldn't be coming back if he didn't. Winning is the only thing he's interested in, but he's taking on young, very hungry guys aged 22, 23, 24 - and it will be fascinating to see if he can keep up with them.

"I've been speaking to people very close to him, and when he was going to make his comeback and tested a two-year-old Ferrari car, they said 'do you know what, we were amazed at how quick he was'. Ross Brawn is absolutely key - Michael Schumacher would not have returned for any other person. He won't know absolutely if he's fit to race until he gets back into a Mercedes Formula 1 car and tests it in January, but he still has it; he still has the speed - and even Michael Schumacher at 99 or 98 per cent is still very fast. Whether that will be enough to sustain over a whole grand prix season against the young guys with all that energy, we'll have to wait and see - but it will be fascinating."

Willi Weber, Schumacher's manager (speaking to Cologne-based newspaper Express):

"Michael is super-fit; [his doctor] said he has made giant progress."